Chesapeake Bay's Blue Crab Population Plummets: Cannibalism and Fish to Blame

It turns out that Chesapeake Bay has something else to worry about aside from its underwater grasses. The bay's blue crab population is at its lowest level in five years, according to Maryland officials. The drop in crabs has prompted tighter catch limits on the region's iconic crustacean.

The findings came after an annual winter survey of Maryland and Virginia waters, which found only 300 million crabs in total; that's down by almost two-thirds from last year when Governor Martin O'Malley announced that the crabs had rebounded from a near population collapse in 2008. The recent announcement is a major setback for those who were working on rebuilding healthy population numbers.

After the near-collapse in 2008, Virginia and Maryland imposed catch limits on blue crabs and disallowed the catching of females. The results made fisheries optimistic; the population rebounded and in the winter of 2011 to 2012, the blue crabs were up by 66 percent from the 461 million in 2010.

Blue crabs are actually strongly linked to the underwater grasses and oyster beds of Chesapeake Bay. The oysters provide the crustaceans with nourishment while the grasses present it with shelter. Unfortunately, the spread of underwater grasses has declined drastically in recent years due to massive storms and excessively warm waters in 2010. In fact, researchers found that the grasses have dropped by as much as 21 percent in 2011.

Surprisingly, though, it turns out that the number of females needed to sustain the population is actually above the usual threshold. Instead, it's the number of juvenile crabs that seem to have disappeared. The recent survey discovered that juveniles dropped by 80 percent since last year.

Fishing doesn't seem to be the cause of this drop, either. Instead, an influx of crab-eating fish--red drum, in particular--may have precipitated the massive population decline. Another possibility is that many of the crabs are turning to cannibalism and are eating the younger and smaller crabs, according to the Baltimore Sun.

Currently, fisheries and officials are taking the drop of population numbers into account. It's likely that the catch will be limited this year, which means less blue crab meat for the rest of us.